Its really simple though just dig a trench fill one end of the trench with a bucket of water and build above and around it. at the end place a pressure plate then connect via redstone line to what ever you want to power. That's the basic concept in a nutshell

its floating around on my desktop being lazy and not uploading itself…. 😛 But fine Tomorrow there will be hopefully two new ones….hopefully but i still need to re upload the improved version of this one first.